IIRC correctly, we did that on 6th Form as well, though it was MSN and things far less obvious than Call of Duty. I believe in the program you set the users security policies in (sorry guess im getting out of touch with windows) you can set whether they can run executables from removable storage. Ill just point out that after our Network Admin cloudly proclaimed that he'd blocked it in an IT lesson, we started using the teachers work postboxes as files to temporarily house the programs. Oh and just to make it worse, this was on 2k mind, even with running executables disabled fro removable media and the users my documents, for some reason if you putt the game files in your home folder and then run a batch script from the flash drive itll still run!

Probably a much longer answer than you wanted. but I ended up slightly more nostalgic than i thought :s

The most effective solution would be confiscation of the memory stick when caught, coupled with loss of computer access priveleges for an appropriate time. All done very publicly to make an example of the miscreant in question & discourage others.

That is assuming you don't want to disable the USB ports on the machines... but to be honest, any technical solution will more than likely either be circumvented or will come back to bite you when you need to run something from a memory stick in an emergency. Better to educate the little horrors that just because they can do something, it doesn't mean they should do it (good citizenship and all that... )

I dont know what your school is like Linuxgirlie, but I have to admit when i was at sixth form the IT admin team adopted a policy similar to that Nigel just suggested, so we took other methods of doing things, the whole year just seemed to team together to annoy this guy, confiscating a 1GB memory stick (back when they were damn expensive) on a permanant basis was more of a catalyst to finding another way to do it. Blocking acocunts seemed quite effective, although there is always the risk they will use someone elses account. Might be worth blocking FTP access if you can, because I used to store the files on my PC at home, ftp in from Windows explorer, run the program, all its files get downloaded to a temporary location and the program runs fine Thinking about it Im gonna stop posting these ideas cos knwoing my luck one of your students will stumble across this page and make life hell for you :S

One solution might be to get very very good at COD and then just join in them and beat them until they get fed up of it. Mind you its not a very constructive solution I admit.
Which version of Windows are you using? I may be able tpo offer some far more constructive solutions, although if it is XP I wont be able to help as much, they upgraded to that in my last year of sixth form so I had far less time to play with it

Best idea would have been to upgrade to Linux I don't know much about COD, but if it is an online game, could you use firewall/router settings to block the ports?
I believe there are some tools for XP that will allow you to do this remotely on all workstations, or for particular user accounts.
Policies can be used to disable removable media.
I know that they don't work on some of my customer's machines.

Disabling the USB ports in bios and password protecting it, disconnecting the front ports, filling them with glue, or using a pair of pliers to make them unusable, are some of the tactics I have seen my customers use to prevent this sort of thing. Of course that means that it is more awkward for you to use them, but you could do it on the most vulnerable ones.
Maybe someone should come up with a USB port lock?
Flash drives are fast becoming a real nuisance on networks, data theft and virus infection are real concerns for companies.

The sig between the asterisks is so cool that only REALLY COOL people can even see it!

Sadly COD isnt an online game, tho it does have a multiplayer, so you could block the prts it uses so they can only play singleplayer. I think it has the option to change the ports in setup though so this is only a temporary fix. Best bet is to block users accounts straight out for doing it, obviously make sure there is a security policy somewhere that they can read stating that this is what will happen. As you are using a mixture of Linux and Windows I dont know what you are using to host all the profiles and home directories, but if it is windows I know for a fact you can disable the ability to run executables on a per user/group basis. So set this for the student group and it should prevent it being an issue for most of the kids. As I said above there are ways around this but it should stop at least 90% from playing these games.

If you want to try a more contraversial way, you could try what my sixth form did to me. Assuming one of the people you catch is fairly computer literate, you can tell them they have to help the network admin team manage the security policies, nothing too interesting, just find some montonous work for them to do that could be a result of game usage, say putting hourly network usage stats for the last month into a spreadsheet. It soon puts people off, they had me looking for a way to block the very game I was caught playing, I may not have tried very hard but I still resented losing three weeks of lunch times (They wouldnt let me stop until I had found at least half a solution, but it took 2 weeks for me to work this out :S )

If you wanted to be more malicious, you could try creating a script that would detect the plug-in of a flash drive, delete all the executables on it, and fill it up with images of the powerpuff girls, or puppies.

Sorry, I'm really having trouble figuring out what the problem is. If I had continually brought games into class my teacher would eventually report me to the year head, who would have gave me a slap on the wrist and sent me on my way. If I continued I would be suspended and ultimately expelled.

You don't need any technical work around with this one, plain and simple discipline will suffice.

Doesnt work nowadays sadly, a lot of the parents around would raise hell for something like that. They just dont seem to take network abuse seriously, mind you in my experience a lot of them dont take vandalism and violence seriously either anymore. This country has gotten way too politically correct. The script sounds like a good idea though you could even write one that adjusts the mixer volume, and plays a sound file whenever someone tries to run an executable from a Flash Drive. That would be open to misuse as well though.

Yeah, but minimum 4 USB ports per machine these days, it's still going to get expensive.

And if the machine uses a USB keyboard or mouse, all the little oik needs to do is to carry a cheapo USB hub around as well and insert it between the device and the machine - heck, I do that for my MP3 player as it's too fat to plug into some USB ports if the adjacent ones are in use; the hub cost me under a fiver on ebay and it's about the size of a Tamagotchi.

lol, they wouldn't last a day, I'm sure they would find a way either to remove, or destroy the USB port that the lock 'n key was used on... and as above we use usb mice/keyboards, ps2 are to easy to break, so they would just remove them...